This invention relates to a pressure detector employed for a medical instrument, such as, a blood processing apparatus for detecting pressures linearly with a pillow type pressure reaction jig.
With a medical instrument, such as, a blood processing apparatus, blood ingredients, such as, corpuscles (blood cells) and plasma taken out of the body, are processed to remove unwanted materials therefrom and are then returned into the body. In other words, the blood is directly taken out of the patient's body, processed and then returned to such body. Therefore, it is essential that the use of the medical instrument will not adversely affect the patient's body. For this purpose, it is necessary to control the blood collection pressure, the plasma pressure, or plasma filtration pressure during blood processing, and the reinfusion or transfusion pressure into the body in such a manner that such pressures are in predetermined, allowable, ranges.
A conventional blood processing apparatus is shown in FIG. 12. In such apparatus, the blood collected, with a blood pump 2, is supplied to a blood filter 3, where such blood is divided into a corpuscle ingredient, and plasma. The plasma is delivered to a plasma filter 5, by a plasma pump 4, where such plasma is filtered to remove unwanted macromolecular ingredients. The condensed plasma is discharged by a plasma discharging pump 6. In this case, a replacing solution 7, corresponding in quantity to the condensed plasma discharged by the plasma discharging pump 6, is supplied with a replacing solution pump 8. The plasma thus processed is mixed with the corpuscle ingredient previously separated. The mixture of the plasma and the corpuscle component is returned into the body through a bubble detector 9.
The blood processing apparatus 1 has five pressure detectors in the above-described blood processing path; a blood collection pressure detector 10, a blood filtration pressure gauge 11, a plasma pressure gauge 12, a plasma filtration pressure gauge 13, and a reinfusion pressure gauge 14, all for detection of the presence or absence of abnormal conditions. These pressure detectors employ a drip chamber 15 as shown in FIG. 13. The drip chamber 15 has an air chamber 16, in its upper portion, communicated, through a pressure leading tube 17, to a pressure sensor 18 of strain gauge type. The pressure leading tube 17 is extended through a filter 19 which permits the flow of air but not of liquid. The air chamber 16 is further connected to a liquid inlet pipe 20 and an air vent pipe 21. The lower end portion of air chamber 16 is connected to a liquid outlet pipe 22. The air vent pipe 21 is for determining the level of liquid in drip chamber 15, and is normally closed.
The pressure in the air chamber 16 of the drip chamber 15 is detected with pressure sensor 18. In other words, in the conventional blood processing apparatus 1, pressure detectors, using the above-described drip chambers 15, are employed to detect a blood collection pressure, blood filtration pressure, plasma pressure, plasma filtration pressure, and reinfusion pressure.
In such conventional pressure detector, using the above-described drip chamber 15, the level of the liquid in the drip chamber 15 changes with the pressure. In order to absorb this change, it is necessary for the chamber to have a volume larger than a certain value. That is, the pressure detector is disadvantageous in that it unavoidably increases the priming volume. Furthermore, in order to operate the blood processing apparatus 1, it is essential to adjust the air vent pipe 21 and, thereby, adjust the level of liquid in drip chamber. That is, it is necessary to set the level of the liquid to the middle of the allowable range in which the level of the liquid in the drip chamber 15 is variable.
In the conventional blood processing apparatus 1, it is necessary to set the level of the liquid in each of the drip chambers 15. Some of the apparatus have three to eight drip chambers. In this case, it is rather troublesome to adjust all of those drip chambers. In addition, such setting of the level of the liquid in the drip chamber can be achieved only by a skilled person. This is one of the factors which lengthen the time required for the preparation of the apparatus.
The pressure detector, using the above described drip chamber 15, suffers from the following difficulty: In the drip chamber 15, sometimes the level of the liquid is abnormally raised for some reason, so that the liquid is caused to flow to the filter 19 provided for preventing the flow of liquid to the pressure sensor 18. However, if the filter 19 is wet, the flow of air is blocked and, as a result of which the pressure detector does not work. This failure greatly affects the functions of other parts of the blood processing apparatus, breaking down the blood processing apparatus, itself, and the medical treatment must be suspended. This is a serious problem and concerns the life of the patient.